see, you need to plug in that x value into the restraint, using that value of lambda
2x = L(8x) -> L=1/4, x=0
2y = L(2y-4) -> y-2=y/L
2z = L(2z-2) -> z-1=z/L
plug these into
4x^2+(y-2)^2+(z-1)^2=4
now look how we can rewrite the restraint: